Streamlined Total Synthesis of Uncialamycin and Its Application to the Synthesis of Designed Analogues for Biological Investigations

Abstract

From the enediyne class of antitumor antibiotics, uncialamycin is among the rarest and most potent, yet one of the structurally simpler, making it attractive for chemical synthesis and potential applications in biology and medicine. In this article we describe a streamlined and practical enantioselective total synthesis of uncialamycin that is amenable to the synthesis of novel analogues and renders the natural product readily available for biological and drug development studies. Starting from hydroxy- or methoxyisatin, the synthesis features a Noyori enantioselective reduction, a Yamaguchi acetylide-pyridinium coupling, a stereoselective acetylide-aldehyde cyclization, and a newly developed annulation reaction that allows efficient coupling of a cyanophthalide and a p-methoxy semiquinone aminal to forge the anthraquinone moiety of the molecule. Overall, the developed streamlined synthesis proceeds in 22 linear steps (14 chromatographic separations) and 11% overall yield. The developed synthetic strategies and technologies were applied to the synthesis of a series of designed uncialamycin analogues equipped with suitable functional groups for conjugation to antibodies and other delivery systems. Biological evaluation of a select number of these analogues led to the identification of compounds with low picomolar potencies against certain cancer cell lines. These compounds and others like them may serve as powerful payloads for the development of antibody drug conjugates (ADCs) intended for personalized targeted cancer therapy.

Strain Prioritization and Genome Mining for Enediyne Natural Products

“…The TNMs are extremely potent against a broad spectrum of cancer cell lines, with subnanomolar 50% inhibitory concentrations (IC 50 s). For example, TNM A is more potent than UCM, particularly against breast cancer cell lines (Table 1A); UCM is currently in preclinical development as an ADC (Chowdari et al, European patent application WO 2013122823 A1) (44). Most impressively, as exemplified with the SKBR-3 breast cancer cell line, TNM A exhibited more rapid and more complete cell killing than AFP and AP-3 (Tables 1B and C), thereby minimizing the development of potential drug resistance (45, 46), supporting the wisdom of exploiting the TNMs as payload candidates for the next generation of anticancer ADCs.…”

The Role of Organic Synthesis in the Emergence and Development of Antibody–Drug Conjugates as Targeted Cancer Therapies

“…Scheme 2summarizes the strategy employed by the Corey group in their total synthesis of maytansine (105), the first to be achieved of this molecule in 1980. [80b] Scheme 2Aindicates, in retrosynthetic format, the chartered synthetic strategy for the synthesis as it evolved, while Scheme 2B provides details for its execution.…”

“…A) Retrosynthetic disconnections;a nd B) total synthesis (1992, Kishi et al). [89] Angewandte Chemie Reviews retrosynthetic disconnections and defined building blocks indicated in Scheme 11 A, the streamlined total synthesis of uncialamycin [105] starting material 254.T his scalable synthesis has been employed to produce,b esides uncialamycin, numerous designed analogues,t wo of which (i.e., 264 and 265)a re highlighted in Scheme 11 Ct ogether with their cytotoxicities against anumber of cancer cell lines. [105] 4.8.…”

The Evolution and Impact of Total Synthesis on Chemistry, Biology and Medicine

“…Our first total synthesis delivered the natural substance in racemic form and allowed its full relative stereochemical assignment, while our second and asymmetric synthesis delivered its natural enantiomeric form and proved its absolute configuration . In our most recent total synthesis of uncialamycin we discovered and employed a much more efficient method for the construction of its anthraquinone moiety and developed a streamlined process for its production (22 linear steps, 11 % overall yield) . Summarized in Figure [from building blocks J – N and intermediates (+)‐ 74 –(+)‐ 77 ], this strategy was employed for the construction of numerous analogues of uncialamycin, some with low picomolar potencies against a variety of tumor cells.…”